(1) Field of the Invention
The present invention relates to a microcamera, and more particularly to a microfilm camera for photographing the images of original documents on reduced scales on films.
(2) Description of the Prior Art
The microcamera has been in existence heretofore as a device for preparing microfilms for use in information retrieval by a reader-printer or the like.
The preparation of microfilms by means of the microcamera involves various sizes of original documents to be photographed such as A3 size and A4 size. Take a 35 mm wide film for example, the half-size frame is standardized to be 31.8 mm.times.22.5 mm and the full-size frame 31.8 mm.times.45 mm. In one method of photographing the original documents in various sizes, the sizes of frames in the film are switched between half size (referenced A) and full size (referenced B) as shown in FIG. 1 of the accompanying drawings. The conventional method in which the frame sizes are switched as above is carried out by providing an aperture member on a projecting optical path extending from the original document to the film for setting a photographing area on the film, which member has opposite ends defining an aperture in the direction of film advance, and moving these opposite ends toward each other (in directions to close the aperture) and away from each other (in directions to open the aperture) in accordance with the orginal document sizes. The opposite ends of the aperture are moved toward each other for setting the photographing area to the half size and away from each other for setting the photographing area to the full size.
However, the above method has the following problems. Firstly, since the opposite ends of the aperture are moved, an end of the original document cannot be used as the basis for setting the original document in position on an original board. Therefore, only the centerline of the original document remains available as the basis for position setting. It is then necessary to determine the centerline of the original document in advance, which results in a very troublesome position setting step. In the case of a microcamera having an autofeed mechanism for advancing the original document particularly, there arises the problem of requiring a complicated construction for detecting and setting the original document and a troublesome control operation.
Secondly, since the opposite ends of the aperture are moved away from each other when photographing an A3 size document after an A4 size document, the image of the A3 size document could be superposed on the image of the A4 size document on an exposed portion of the film. In order to avoid this inconvenience, the film must be further advanced in an additional step by an adequate length to prevent the double exposure on the exposed portion of the film. This additional step is taken separately from a film advance operation carried out every time the original document is changed. However, such a film advance control is troublesome and requires a complicated construction.
Thirdly, since the opposite ends of the aperture are moved toward each other when photographing an A4 size document after an A3 size document, too large a blank space is formed between the image of the A3 size document and that of the A4 size document on the exposed portion of the film. The film must be moved backward to avoid this inconvenience and provide an appropriate blank space. Such an operation involves a troublesome control and a complicated construction as noted in connection with the second problem above.